Modern railroad locomotives are complex vehicles containing multiple operating systems including sophisticated computerized controls responsive to a large number of input variables. A typical electro-motive railroad locomotive is propelled by a plurality of AC or DC traction motors connected to respective drive axles, with the electrical energy for the motors being supplied by an on-board generator powered by a diesel engine.
Locomotives are assembled in a number of different configurations so as to satisfy one or more respective mission requirements served by a railroad. One may appreciate that the operational requirements for over-the-road hauling are significantly different than those for switchyard operation. For example, a switcher locomotive generally moves a relatively small number of cars across a mostly flat area at low speeds, whereas road-hauling locomotives must be capable of moving a train at relatively high speeds across terrain that may include significant changes in topography. A switcher locomotive may also spend a significant amount of time idling, whereas road locomotives must operate for long periods at high power levels.
Railroad mission requirements are affected by numerous variables including customer demand, weather, equipment availability, personnel availability, government regulations, etc., and it is often impossible for a railroad dispatcher to make available the best-suited locomotive for a particular mission. For example, even a single mission as simple as moving a train from point A to point B may involve mission demands that vary significantly with the geography of the railroad track, such as different government emission regulations at different points along a railroad track. As a result, a locomotive originally assembled with the configuration suited for an initial intended mission will provide less-than-optimal configuration when placed into service for another and different mission, and typically the best a dispatcher is able to do is to provide a locomotive that presents a good compromise of capabilities to meet a range of different (and often competing) mission requirements.